The present embodiments relate to a magnetic resonance arrangement having a plurality of antenna elements disposed around a measurement chamber.
In a magnetic resonance device, a body to be examined may be exposed to a relatively high basic magnetic field (e.g., of 3 or 7 Tesla) with the aid of a basic magnetic field system. A magnetic field gradient is additionally applied with the aid of a gradient system. Radio-frequency magnetic resonance excitation signals (RF signals) are transmitted via a radio-frequency transmission system using suitable antennas, the aim being to tilt the nuclear spins of specific atoms resonantly excited by the radio-frequency field through a defined flip angle with respect to the magnetic field lines of the basic magnetic field. The radio-frequency excitation or the resulting flip angle distribution is also referred to as nuclear magnetization. During the relaxation of the nuclear spins, radio-frequency signals (e.g., magnetic resonance signals) are emitted, are received using suitable receive antennas, and are processed further. The desired image data may be reconstructed from raw data acquired in this way. The radio-frequency signals for producing the nuclear spin magnetization may be transmitted using a “whole-body coil” or a “bodycoil”. A typical structure for this is a cage antenna (e.g., a birdcage antenna) consisting of a plurality of transmit rods that are disposed running parallel to the longitudinal axis around a patient chamber of a tomograph apparatus, in which a patient is positioned during the examination. At a front side, the antenna rods are connected to one another in the shape of a ring.
Individual antenna rods may consist of conductor tracks equipped with reactance components (e.g., capacitive elements) having specific predetermined values. The ring segments interconnecting the antenna rods are structured as conductor tracks having specific reactance components. Apart from a frontal annular connection, it is also possible in the case of relatively long cage antennas to connect the antenna rods in addition in a ring shape at one or more points in a central region.
Local coils that are directly attached to the body of the patient may be used for receiving the magnetic resonance signals. The local coils may include a group of conductor loops (e.g., an antenna array), the antenna conductor loops being operable individually. The antenna array may form a relatively large surface antenna on the body of the examination subject or patient. The antenna elements may be constructed so as to be particularly sensitive and capable of also receiving weak signals that are amplified and may be used as raw data. An advantage of such an antenna array having a plurality of individually operable conductor loops is that within the scope of parallel imaging methods, the image acquisition process is speeded up considerably, and as a result, the patient's exposure to radiation may be reduced. Many patients find it unpleasant having relatively large local coil arrays attached to their body. This may be true of patients of a claustrophobic disposition who already feel confined inside the patient tunnel.
The antenna architecture known as a “remote body array” (also referred to in the following as RBA for short) may be a suitable solution for implementing a magnetic resonance device having a minimum requirement for local coils. An RBA consists of an array of individual antenna conductor loops disposed at a distance from the patient within the measurement chamber. Conventionally, the RBA is constructed in the measurement chamber inside the bodycoil. An attempt is made to position the RBA as close as possible to walls of the measurement chamber so that as much free space as possible is available to the patient. The RBA disposed within the measurement chamber also restricts the free space for the patient.